The influence of six antimicrobial agents on the lightfastness of acid dyes and yellowing in nylon 6 was investigated. There were 2 silicone quaternary ammonium salts, an organo-tin, a phenolic mixture, a coapplication of quaternary ammonium salt/organo-tin evaluated. The finished specimens were exposed to xenon light, and color change was instrumentally evaluated. The quaternary ammonium salt/organo-tin and phenol mixture caused the greatest color change in the dyed and undyed nylon. The organo-tin treatment applied alone had minimal or no effect.